# ---
# title: 852. Peak Index in a Mountain Array
# id: problem852
# author: Indigo
# date: 2021-06-15
# difficulty: Easy
# categories: Binary Search
# link: <https://leetcode.com/problems/peak-index-in-a-mountain-array/description/>
# hidden: true
# ---
# 
# Let's call an array `arr` a **mountain**  if the following properties hold:
# 
#   * `arr.length >= 3`
#   * There exists some `i` with `0 < i < arr.length - 1` such that: 
#     * `arr[0] < arr[1] < ... arr[i-1] < arr[i] `
#     * `arr[i] > arr[i+1] > ... > arr[arr.length - 1]`
# 
# Given an integer array arr that is **guaranteed** to be a mountain, return any
# `i` such that `arr[0] < arr[1] < ... arr[i - 1] < arr[i] > arr[i + 1] > ... >
# arr[arr.length - 1]`.
# 
# 
# 
# **Example 1:**
# 
#     
#     
#     Input: arr = [0,1,0]
#     Output: 1
#     
# 
# **Example 2:**
# 
#     
#     
#     Input: arr = [0,2,1,0]
#     Output: 1
#     
# 
# **Example 3:**
# 
#     
#     
#     Input: arr = [0,10,5,2]
#     Output: 1
#     
# 
# **Example 4:**
# 
#     
#     
#     Input: arr = [3,4,5,1]
#     Output: 2
#     
# 
# **Example 5:**
# 
#     
#     
#     Input: arr = [24,69,100,99,79,78,67,36,26,19]
#     Output: 2
#     
# 
# 
# 
# **Constraints:**
# 
#   * `3 <= arr.length <= 104`
#   * `0 <= arr[i] <= 106`
#   * `arr` is **guaranteed** to be a mountain array.
# 
# 
## @lc code=start
using LeetCode

peak_index_in_mountain_array(arr) =
    searchsortedfirst(1:(length(arr) - 1), length(arr) - 1; by=i -> arr[i] > arr[i + 1])

## @lc code=end
